Then I had to re-encode to a freer format that took ages and looked crap.

I tried using vp8 and after many attempts I got a reasonable webm screen capture. Running sound and video capture in the same command failed to grab all the sound but I discovered that running them as seperate commands worked fine!

I added both commands to a script and muxed them without the need to re-encode.

Capture screen and rename with date and time year-month-day-hour-seconds in a libre format.